Communications throughput with multiple physical data rate transmission determinations

ABSTRACT

An access point of a communications network is configured to receive a multicast or broadcast packet from a source. The access point converts the multicast or broadcast packet into a unicast packet addressed to a station associated with the access point. The access point then transmits the unicast packet over the communications network from the access point to the station. The access point further may determine a minimum data rate by which the access point may transmit the multicast or broadcast packet to the station and determines an effective unicast rate for transmitting the unicast packet to the station. If the effective unicast rate does not exceed the minimum data rate, the access point does not transmit the unicast packet to the station and transmits the multicast or broadcast packet.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional and claims the priority of U.S. patentapplication Ser. No. 11/232,196, entitled “Systems and Methods forImproved Data Throughput in Communications Networks,” filed on Sep. 20,2005, which claims the benefit of U.S. Provisional Patent ApplicationNo. 60/625,331 entitled “Systems and Methods for Improved DataThroughput in Wireless Local Area Networks,” filed on Nov. 5, 2004, thesubject matter of which are hereby incorporated by reference.

This application is related to co-pending U.S. patent application Ser.No. 11/010,076 entitled “System and Method for an Omnidirectional PlanarAntenna Apparatus with Selectable Elements,” filed on Dec. 9, 2004, U.S.patent application Ser. No. 11/022,080 entitled “Circuit Board Having aPeripheral Antenna Apparatus with Selectable Antenna Elements,” filed onDec. 23, 2004, and U.S. patent application Ser. No. 11/041,145 entitled“System and Method for a Minimized Antenna Apparatus with SelectableElements,” filed on Jan. 21, 2005, the subject matter of which arehereby incorporated by reference.

This application is also related to co-pending U.S. patent applicationSer. No. ______, “Improved Communications Throughput With Unicast PacketTransmission Alternative,” filed on Nov. 16, 2007, which is itself adivisional of U.S. patent application Ser. No. 11/232,196, “Systems andMethods for Improved Data Throughput in Communications Networks,” filedon Sep. 20, 2005.

The disclosures of the aforementioned applications are incorporatedherein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to communications networks andmore particularly to systems and methods for increased data throughputin communications networks.

2. Description of the Prior Art

Demand for multimedia applications, including audio and video data, israpidly increasing. Some of the more popular uses of multimedia arereal-time interactive applications, such as video and audio streaming,Internet Protocol TV (IPTV), transmission of lectures or speeches to aremote audience, and animated simulations. Even when data compression isused, multimedia applications require large amounts of bandwidth.

In an IEEE 802.11 wireless local area network (LAN), broadcast, ormulticast packet transmission enables bandwidth-intensive multimediaapplications to simultaneously transmit audio and video data packets toeach receiving node associated with a group of the wireless LAN.Broadcast packets are transmitted to all receiving nodes of the wirelessLAN, whereas multicast packets are transmitted to two or more, but fewerthan all, of the receiving nodes of the wireless LAN.

In the wireless LAN, a source node may transmit (e.g., via Ethernet)multicast packets to a multicast-enabled access point, and the accesspoint sends the multicast packets via wireless transmission todestination receiving nodes that have identified themselves as part ofthe multicast group.

The access point of the wireless LAN may also support unicast packettransmission. For unicast transmission in the wireless LAN, the accesspoint transmits one or more unicast packets to the receiving nodeidentified by an intended destination address included in the unicastpackets. After receiving the unicast packet, the receiving nodetransmits (approximately 9 μs later) an 802.11 acknowledgement (ACK)packet back to the access point. The 802.11 ACK mechanism providesreliable data transmission in the typically highly interfered 802.11wireless network by confirming to the access point that the unicastpacket was received.

A limitation with transmitting multicast packets in the wireless LAN isthat the 802.11 ACK does not provide a reliable mechanism for ensuringthat the receiving nodes actually received the multicast packets. Forexample, if the 802.11 access point were to transmit one or moremulticast packets to a number of receiving nodes, and each of thereceiving nodes were to respond essentially simultaneously with 802.11ACK packets, the multiple ACK packets received by the access point wouldcomprise “noise” during the period of the multiple simultaneous 802.11ACKs. To the access point, these multiple simultaneous 802.11 ACKs areundecipherable. This condition may be referred to as a “multiple ACKproblem.”

Another limitation with transmitting multicast packets is that thewireless LAN may be limited in the bandwidth used for multicast packets.Because of the multiple ACK problem, the IEEE 802.11 specification formulticast dictates that transmission of multicast packets occur at aminimum allowable physical data rate. Because the receiving nodes may beat various distances from the source of the transmission, and mayexperience various interference levels, transmitting at the minimumallowable physical data rat improves the probability of reception of themulticast packets by each receiving node. For example, an 802.11 accesspoint transmits multicast packets at a minimum allowable physical datarate of 1 Mbps for 802.11b and 6 Mbps for 802.11a. The receiving nodesdo not transmit 802.11 ACK packets to verify reception of the multicastpackets. Thus, without the 802.11 ACK mechanism, there is noverification of reception of the multicast packets.

Further, transmitting at the minimum allowable physical data rateunder-utilizes available bandwidth in the wireless LAN, which otherwiseis capable of supporting much higher data rates. In addition,transmitting at the minimum allowable physical data rate may make thewireless LAN unsuitable for applications that require high ratecommunication, such as multimedia applications.

SUMMARY OF THE INVENTION

The invention addresses the above problems by providing systems andmethods for improved data throughput in communications networks. Anaccess point of a communications network of one embodiment receives amulticast or broadcast packet from a source. The access point convertsthe multicast or broadcast packet into a unicast packet addressed to astation associated with the access point. The access point thentransmits the unicast packet over the communications network from theaccess point to the station. By converting the multicast or broadcastpacket into one or more unicast packets, the access point achievesimproved data throughput in the communications network by sending theunicast packet at higher data rate than would otherwise be possible bytransmitting the multicast or broadcast packet to the station.Additionally, the unicast packet provides for reliable delivery of datain the multicast or broadcast packet in communications networks wherethe unicast packet is acknowledged.

In some embodiments, the communication network comprises an 802.11wireless network. The access point may determine the station from a listof one or more stations associated with the access point. The accesspoint may determine a minimum data rate by which the access point maytransmit the multicast or broadcast packet to the station and determinean effective unicast rate for transmitting the unicast packet to thestation. The access point then may not transmit the unicast packet tothe station and may transmit the multicast or broadcast packet to thestation if the effective unicast rate does not exceed the minimum datarate.

The access point may also determine an antenna configuration on which totransmit to the station and determine a physical data rate at which totransmit to the station. The access point then may transmit the unicastpacket on the antenna configuration and at the physical data rate over awireless network from the access point to the station. In still furtherembodiments, the access point determines that the station acts as thesource and does not transmit the unicast packet to the station. Theaccess point may query the station to determine an address for thestation and may map an address of the multicast or broadcast packet tothe address of the station. The access point may also associate thestation to an address of the multicast or broadcast packet based on ajoin request transmitted from the station to the source.

A method is provided comprising receiving into an access point amulticast or broadcast packet from a source and converting the multicastor broadcast packet into a unicast packet addressed to stationassociated with the access point. The method also includes transmittingthe unicast packet over the communications network from the access pointto the station. The multicast or broadcast packet may comprise a UserDatagram Protocol (UDP) networking message. The multicast or broadcastpacket may also comprise a multicast control packet.

An alternative method comprises receiving into an access point of acommunications network a multicast or broadcast packet from a source,determining a first rate by which the access point may transmit themulticast or broadcast packet to a first station associated with theaccess point, determining a second rate by which the access point maytransit the multicast or broadcast packet to a second station associatedwith the access point, and transmitting the multicast or broadcastpacket to the first station and the second station at the lower of thefirst rate and the second rate. Advantageously, the access point maydetermine a higher data rate than a minimum physical data rate specifiedfor the communications network at which the access point may transmitthe multicast or broadcast packet to the first station and the secondstation.

A first node of a communication network, in one embodiment, fortransmitting to a second node of the communication network is configuredto determine a first rate for transmitting a multicast or broadcastpacket. The first node also determines a second rate for transmitting tothe second node one or more unicast packets resulting from conversion ofthe multicast or broadcast packet into the one or more unicast packets.The first node then transmits the one or more unicast packets to thesecond node if the second data rate exceeds the first data rate andotherwise transmits the multicast or broadcast packet to the secondnode.

Advantageously, the first node converts the multicast or broadcastpacket, when appropriate, to one or more unicast packets and transmitsthe one or more unicast packets sequentially to the second node at ahigher data rate than the minimum physical data rate specified formulticast or broadcast transmission. The first node may comprise amulticast-enabled access point. In some embodiments, the first nodedetermines a third rate by which the first node may transmit themulticast or broadcast packet to a third node of the communicationsnetwork and transmits over the communications network the multicast orbroadcast packet to the second node and the third node at the lower ofthe first rate and the third rate.

Therefore, the systems and methods may provide reliable transmission ofthe multicast or broadcast packet over the wireless LAN by convertingthe multicast or broadcast packet to the one or more unicast packets andservicing corresponding acknowledgement packets from the station. Afurther advantage is that the systems and methods may determine not toconvert the multicast or broadcast packet, and may transmit themulticast or broadcast packet over the wireless LAN at a higher datarate than the minimum physical data rate that the station may reliablyreceive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a system for multicasttransmission in a wireless local area network, in accordance with oneembodiment of the present invention;

FIG. 2 illustrates an exemplary method for multicast or unicasttransmission in the wireless local area network of FIG. 1, in accordancewith one embodiment of the present invention; and

FIG. 3 illustrates an exemplary timing diagram illustrating conversionof multicast packets into unicast packets as described with respect toFIGS. 1-2, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

The systems and methods disclosed herein enable data throughput incommunication networks greater than that which is provided in the priorart. For example, the system and method disclosed herein supportbandwidth-intensive multimedia applications over wireless LANs. In thedisclosure, nodes of a communication network may be referred to as ahost, a source, a destination, a node, a receiving node, an accesspoint, and a station. The references should not be considered in alimiting sense, as it is understood that the present invention is in noway limited to only the embodiments illustrated. For example, a“receiving node” is in no way limited to the function of receiving only.Additionally, the term group packet includes a multicast packet, abroadcast packet, and any packet whose destination address indicates oneor more addresses and/or nodes of the communications network.

According to one embodiment, a wireless local area network (LAN)comprises an access point configured to receive a multicast or broadcastpacket from a source. The multicast or broadcast packet is addressed toa group comprising one or more nodes of a communications network (e.g.,stations associated with the access point of the wireless LAN). Theaccess point determines whether to convert the multicast or broadcastpacket into one or more unicast packets for sequential transmission tothe one or more nodes or whether to transmit the multicast or broadcastpacket to the group. If the access point transmits the multicast orbroadcast packet without conversion, the access point may determine alowest common denominator data rate based on data rates for transmittingmulticast or broadcast packets to the one or more nodes and transmitsthe multicast or broadcast packet to the group at the lowest commondenominator rate.

FIG. 1 illustrates a block diagram of a system 100 for multicast packettransmission in a wireless local area network, in accordance with oneembodiment of the present invention. The system 100 comprises a sourcenode 110, a network link 115, an access point 120, receiving nodes 130,140, and 150, wireless links 135, 145, and 155, and a group 160comprising two or more of the receiving nodes (e.g., the receiving nodes130 and 140). The source node 110 is configured to communicate with theaccess point 120 over the network link 115. The access point 120 isconfigured to communicate with the receiving nodes 130-150 over thewireless links 135-155 that form the wireless LAN.

The source node 110 is any device capable of network communicationincluding unicast or multicast packet transmission with the access point120 over the network link 115. The source node 110 may comprise, forexample, a personal computer, a server, a network attached storagedevice, or a network video distribution device. The source node 110 maysupport networking protocols such as Transmission ControlProtocol/Internet Protocol (TCP/IP), User Datagram Protocol (UDP/IP),and/or Internet Group Management Protocol (IGMP), and may supportunicast, multicast, and/or broadcast packet transmission of networkdata.

The source node 110 is configured to transmit one or more group packetsaddressed to the group 160 (e.g., one or more multicast or broadcastpackets) over the network link 115. The network link 115 may be a wiredor wireless network link. In one embodiment, the network link 115comprises a UDP/IP connection. In one example, the source node 110comprises an IPTV video server (not shown) that transmits the multicastpackets, providing a remote video stream to the group 160 through theaccess point 120. Although discussed in regard to multicasttransmission, the group packets may comprise a packet whose destinationaddress specifies all (i.e., broadcast), or less than all (i.e.,multicast) of the receiving nodes 130-150.

The receiving nodes 130-150 each comprise any device capable ofreceiving network communication from the source node 110 through theaccess point 120 over the wireless links 135-155. The receiving nodes130-150 may comprise devices such as personal computers, PDAs, cellphones, and/or internet enabled televisions. In one example, thereceiving nodes 130-140 of the group 160 may comprise TV set-top boxesconfigured to receive a video stream provided by the IPTV server at thesource node 110 to the group 160. Although described as the source node110 and the receiving nodes 130-150, it should be noted that the sourcenode 110 may also be the destination node of a data packet as well asthe receiving nodes 130-150 may also be the source node of a datapacket.

As described further herein, the access point 120 is configured totransmit the video stream to the receiving node 130 and the receivingnode 140 either simultaneously as a multicast packet, or sequentially asone or more unicast packets to each of the receiving nodes 130 and 140.The access point 120 is virtually any device capable of acting as abridge in a peer-to-peer connection in the wireless LAN or as a bridgebetween the network link 115 and the wireless links 135-155. The accesspoint 120 may be configured to convert the multicast packet into one ormore unicast packets, as discussed further with respect to FIG. 2. Theaccess point 120 may include a processor, a memory, and additionalcircuitry that provides or assists in providing the bridge and/or themulticast packet conversion. The access point 120 may use the IEEE802.11 protocol, such as 802.11a or 802.11b, to communicate with thereceiving nodes 130-150. It will be appreciated that the access point120 may incorporate other wireless protocols, such as 802.11g, 802.16,or Bluetooth.

The access point 120 may support multicast control protocols, such asIGMP, and may be configured as a multicast-enabled router. A multicastcontrol protocol enables the access point 120 to determine from thereceiving nodes (e.g., the receiving nodes 130-150) which group(s)(e.g., the group 160) the receiving nodes 130-150 are associated with.Some examples of multicast control protocols are IGMP,Protocol-Independent Multicast (PIM), Real-Time Streaming Protocol(RTSP), Multiprotocol Border Gateway Protocol (MBGP), Multicast SourceDiscovery Protocol (MSDP), Simple Service Discovery Protocol (SSDP), andSource Specific Multicast (SSM). For example, the receiving node 130 maysend a multicast control protocol packet to the access point 120 tochange the channel for an IPTV multicast stream received from the sourcenode 110. The multicast control protocol packet informs the access point120 that the receiving node 130 is interested in receiving group packetsfor the selected channel.

The access point 120 of some embodiments is further configured tomaintain information about “associated nodes.” Associated nodes aredevices that have negotiated a wireless communication link (e.g., thewireless link 135) with the access point 120. For example, when thereceiving node 130 initially associates with the access point 120 tonegotiate the wireless link 135, the receiving node 130 provides a MediaAccess Control (MAC) or hardware address that uniquely identifies thereceiving node 130. The receiving node 130 may also provide a list ofallowable physical data rates (e.g., 1 Mbps-54 Mbps) at which it maycommunicate with the access point 120. The access point 120 may storesuch information about the associated nodes in memory, for example.

As described further herein, the system 100 improves multicast datathroughput in the wireless LAN because the access point 120 of oneembodiment is configured to convert the multicast packet addressed tothe group 160 into one or more unicast packets addressed to thereceiving nodes 130-140. The access point 120 may transmit the one ormore unicast packets sequentially to the receiving nodes 130-140 at ahigher data rate than the minimum data rate used for 802.11 multicasttransmission. Further, the access point 120 of this embodiment wouldensure reliable transmission of the converted multicast packet becausethe access point 120 would be able to service 802.11 ACK packetsgenerated by the receiving nodes 130-140. In some embodiments, theaccess point 120 may determine not to convert the multicast packet intoone or more unicast packets, but instead may transmit the multicastpacket to the receiving nodes of the group 160 at a relatively higherdata rate than the minimum allowable physical data rate used for 802.11multicast packet transmission.

FIG. 2 illustrates an exemplary method for multicast or unicasttransmission in the wireless local area network of FIG. 1, in accordancewith one embodiment of the present invention. The steps of the exemplarymethod are described as occurring in particular order, but it will beappreciated that certain steps may be rearranged to provide a similarresult. The method determines whether to convert a multicast packet intoone or more unicast packets or whether to transmit the multicast packet.The method also determines at what rate to transmit the multicast packetand the one or more unicast packets. The method begins with the accesspoint 120 already associated with receiving nodes 130-150.

In step 205, the access point 120 receives a first join request (e.g., amulticast control protocol packet such as an IGMP join request) from thefirst receiving node (e.g., the receiving node 130) containing a firstaddress for the receiving node 130. The access point 120 uses the joinrequest to correlate the receiving node 130 with the address of thegroup 160. In IGMP, a multicast client (e.g., the receiving node 130)joins a multicast group (e.g., the group 160) to enable group receptionof a multicast traffic stream. When the access point 120 receives theIGMP join request from the receiving node 130, the access point 120inspects the IGMP packet and determines the required join information.

In this embodiment, the access point 120 does not itself use the IGMPprotocol. Regardless, the system 100 takes advantage of the fact thatthe IGMP join requests from the receiving nodes 130-140 to the sourcenode 110 pass through the access point 120. The access point 120“sniffs” or samples the IGMP join requests to map the hardware (MAC)address of the receiving nodes 130 and 140 with the address of the group160. In some embodiments, the access point 120 “speaks” the IGMPprotocol. The access point 120 may map the IP addresses (instead of theMAC addresses) of the receiving nodes 130 and 140 to the address of thegroup 160.

In the alternative to sniffing or speaking IGMP or other controlprotocols from the receiving nodes 130-150, the access point 120 maymaintain a map that contains the hardware addresses of all or a subsetof the receiving nodes 130-150 that are associated with the access point120. The access point 120 may use the map to query the receiving nodes130-150 to determine which of the receiving nodes 130-150 are interestedin receiving multicast traffic addressed to the group 160. These maps ofMAC addresses or IP addresses allow the access point 120 to convert themulticast packet received from the source node 110 and addressed to thegroup 160 into one or more unicast packets addressed to the receivingnodes 130-140 of the group 160.

In step 210, the access point 120 maps the first address of thereceiving node 130 from the IGMP packet to the address of the group 160.In step 215, the access point 120 receives a second join request (e.g.,a second IGMP join request) from a second receiving node (e.g., thereceiving node 140). In step 220, the access point 120 maps a secondaddress of the receiving node 140 to the address of the group 160.

In step 225, the access point 120 receives the multicast packetaddressed to the group 160. In step 230, the access point 120 determinesa first data rate (e.g., 54 Mbps) by which the access point 120 mayreliably transmit (e.g., including the 802.11 ACK mechanism) one or moreunicast packets to the receiving node 130. In step 235, the access point120 determines a second data rate (e.g., 24 Mbps) by which the accesspoint 120 may reliably transmit one or more unicast packets to thereceiving node 140. Although not depicted, in some embodiments theaccess point 120 may determine additional (e.g., a third or more) datarates by which the access point 120 may reliably transmit one or moreunicast packets to a third receiving node (e.g., the receiving node 150which would be part of the group 160).

In step 240, the access point 120 determines an effective unicast rate.As discussed further with respect to FIG. 3, the effective unicast ratecorresponds to a combined rate for converting the multicast packet intoone or more unicast packets and sending the one or more unicast packetsto the receiving nodes 130 and 140 of the group 160 at the first andsecond (and third . . . ) data rates. The effective unicast rate dependson the total number of bits included in the unicast packets, includingadditional data packet overhead (e.g., additional bits in the unicastpacket as compared to the multicast packet). The effective unicast ratealso depends on computational time associated with converting themulticast packet into one or more unicast packets. The effective unicastrate is further based on the duration for reception and processing ofACK packets from the receiving nodes of the group 160. Further, theeffective unicast rate is based on the number of receiving nodes in thegroup 160, because each additional receiving node in the group 160proportionally lowers the effective unicast rate. One method fordetermining the effective unicast rate is presented in co-pending U.S.patent application entitled “System and Method for TransmissionParameter Control for an Antenna Apparatus with Selectable Elements,”the subject matter of which is hereby incorporated by reference.

As described further, rather than converting the multicast packet tounicast packets, the access point may transmit at a “lowest commondenominator rate” to the group 160. For example, the lowest commondenominator rate may be higher than the effective unicast rate,particularly with a large number of receiving nodes in the group 160each receiving at a relatively high rate. For example, the group 160 maycomprise the receiving nodes 130, 140, and 150. The receiving node 130may receive packets at a physical data rate of 54 Mbps, the receivingnode 140 may receive packets at a physical data rate of 54 Mbps, and thereceiving node 150 may receive packets at a physical data rate of 54Mbps. The lowest common denominator rate for this example is 54 Mbps,which may be higher than the effective unicast rate. In step 245, theaccess point 120 determines the lowest common denominator rate (LCDR)for transmitting the multicast packet simultaneously to the receivingnodes of the group 160.

In steps 250-295, the access point 120 determines whether to transmitunicast or multicast packets, and at what rate to transmit the unicastor multicast packets. Specifically, in steps 250-275, the access point120 may determine to convert the multicast packet into one or more firstunicast packets addressed to the receiving node 130 and one or moresecond unicast packet addressed to the receiving node 140 fortransmission. Alternatively, in steps 285-295, the access point 120 maydetermine to transmit the multicast packet simultaneously to thereceiving nodes 130-140 of the group 160 and not convert the multicastpacket into unicast packets. Further, in steps 285-295 the access point120 determines whether to transmit at the lowest common denominator rateif the lowest common denominator rate is higher than the minimumallowable physical data rate.

In step 250, the access point 120 determines if the effective unicastrate exceeds the lowest common denominator rate. For example, in an802.11a wireless LAN with the receiving nodes 130, 140, and 150 in thegroup 160, the first data rate may be 54 Mbps, the second data rate maybe 6 Mbps, and the third data rate may be 54 Mbps. The effective unicastrate, given the number of data bits in the unicast packets, packetoverhead, conversion processing time, and the like may be 11.5 Mbps, forexample. Accordingly, the effective unicast rate of 11.5 Mbps exceedsthe lowest common denominator rate of 6 Mbps (i.e., the minimumallowable physical data rate for 802.11a), so the access point 120 willconvert the multicast packet into one or more unicast packets in steps255-275.

In step 255, the access point 120 converts the multicast packet to afirst unicast packet addressed to the receiving node 130. In step 260,the access point 120 transmits the first unicast packet to the receivingnode 130 at the first data rate. After transmission of the first unicastpacket, in step 265 the access point 120 may delay for a predetermineddelay period before converting the multicast packet into a secondunicast packet and transmitting the second unicast packet to thereceiving node 140 in steps 270-275. The delay period is computed toallow the receiving node 130 sufficient time to generate an 802.11 ACKthat the access point 120 may receive to verify reliable transmissionand reception of the first unicast packet. The access point 120 maycompute the delay period based on several factors. For example, theaccess point 120 may compute the delay based on computational timeneeded by the access point 120 to convert the multicast packet into thefirst unicast packet. The delay may include data packet overhead (e.g.,additional bits in the first unicast packet that reduce the first datarate to a relatively lower “user” data rate). Further, the access point120 may retransmit the first unicast packet to the receiving node 130 ifthe access point 120 does not receive the 802.11 ACK from the receivingnode 130 for the first unicast packet, adding to the delay.

In step 270, the access point 120 converts the multicast packet from thesource node 110 into a second unicast packet addressed to the receivingnode 140. In step 275, the access point 120 transmits the second unicastpacket at the second data rate to the receiving node 140. In similarfashion to the method described above with respect to steps 260-265 forthe first unicast packet, the access point 120 awaits an 802.11 ACK fromthe receiving node 140 to ensure reliable transmission and reception ofthe second unicast packet. The access point 120 may retransmit thesecond unicast packet to the receiving node 140 if the access point 120does not receive the 802.11 ACK from the receiving node 140. Althoughnot depicted, the steps 265 to 275 may be repeated for additional (e.g.,third . . . ) receiving nodes in the group 160.

Optionally, the access point 120 may determine in step 260 and step 275whether one of the receiving nodes of the group 160 comprises amulticast data transmitter. For example, if the receiving node 130 actsas the source node 110 for sending the multicast packet through theaccess point 120 to the receiving nodes 140 and 150 of the group 160,the access point 120 need not retransmit the converted unicast packetback to the receiving node 130. Although sending the unicast packet backto the receiving node 130 is legitimate practice in 802.11, doing sowastes network bandwidth.

At step 250, if the effective unicast rate does not exceed the lowestcommon denominator rate, the access point 120 may determine not toconvert the multicast packet into one or more unicast packets forsequential transmission to each receiving node in the group 160.Accordingly, in step 285, the access point 120 determines whether theLCDR exceeds the minimum allowable data rate. For example, if thereceiving node 130 is capable of receiving at 54 Mbps and the receivingnode 140 is capable of receiving at 24 Mbps, the LCDR of 24 Mbps exceedsthe minimum allowable data rate of 6 Mbps. Accordingly, in step 290 theaccess point 120 will transmit the multicast packet to the group 160 atthe LCDR of 24 Mbps. Alternatively, at step 285 if the receiving node130 is capable of receiving at 54 Mbps and the receiving node 140 iscapable of receiving at only 6 Mbps, for example, the LCDR does notexceed the minimum allowable data rate of 6 Mbps. Accordingly, in step295, the access point 120 will transmit the multicast packet to thegroup 160 at the minimum allowable data rate of 6 Mbps.

The methods described with respect to FIG. 2 advantageously achievehigher data throughput than traditional multicast transmission, byconverting multicast packets in the access point 120 into one or moreunicast packets that may be transmitted sequentially to each receivingnode of the group 160 at a relatively higher data rate. Further,converting the multicast packet into unicast packets affords higher datatransmission reliability because the unicast packets are verified by ACKresponses from each receiving node of the group 160. Additionally, ifthe access point 120 determines not to convert multicast packets intounicast packets, the access point 120 may transmit the multicast packetat the lowest common denominator rate, which is a higher physical datarate than the minimum allowable physical data rate defined in the IEEE802.11 standard.

Although FIGS. 1 and 2 generally describe multicast data flow from thesource node 110 to the group 160 (i.e., left to right in FIG. 1), themethods described with respect to FIG. 2 are applicable to multicastcontrol protocol packets that flow in the opposite direction (e.g., fromright to left in FIG. 1). For example, the system 100 may include asource node (e.g., the receiving node 130) configured to transmit agroup packet to a destination node (e.g., the access point 120). Thereceiving node 130 sends a multicast control protocol packet, such as anIGMP join request, over the wireless link 135 to the access point 120 tojoin a group (e.g., group 160) receiving an IPTV multimedia multicaststream. To provide more effective use of the available bandwidth of thewireless link 135, and to provide reliable transmission of the multicastcontrol protocol packet, the receiving node 135 may convert themulticast control protocol packet to one or more unicast packets fortransmission to and acknowledgement by the access point 120.

In one example, the receiving node 130 determines a first data rate fortransmitting the group packet and determines a second data rate basedupon converting the group packet to a unicast packet addressed to theaccess point 120. The receiving node 130 transmits the unicast packet atthe second data rate through the wireless link 135 to the access point120 if the first data rate for transmitting the group packet is lessthan the second data rate for transmitting the unicast packet. Asdiscussed herein, the receiving node 130 transmits the unicast packet ata higher physical data rate than specified for multicast transmission.Upon receipt of the unicast packet, the access point 120 sends an ACK toacknowledge receipt of the unicast packet.

If the first data rate for transmitting the group packet is greater thanthe second data rate for transmitting the unicast packet, the receivingnode 130 may transmit the group packet through the wireless link 135. Aspreviously discussed, the receiving node 130 may transmit the grouppacket at the lowest common denominator rate. The access point 120 thenreceives the group packet and processes the multicast control protocolpacket. Therefore, in these embodiments, the receiving node 130 and theaccess point 120 individually determine whether transmitting the grouppacket or converting the group packet to one or more unicast packetsallows more effective use of the available bandwidth and reliabletransmission.

FIG. 3 illustrates an exemplary timing diagram comparing the conversionof the multicast packet into one or more unicast packets, as describedin FIGS. 1-2, as compared to multicast packet transmission, inaccordance with one embodiment of the present invention. A first timeinterval 310 indicates the time needed for the access point 120 toconvert the multicast packet received from the source node 110 into thefirst unicast packet and transmit the first unicast packet to thereceiving node 130, for example, at 54 Mbps. It will be appreciated thatthe time interval 310 may vary depending upon at least the first datarate, the number of data bits in the first unicast packet, and theconversion time needed by the access point 120 to convert the multicastpacket into the first unicast packet. After the first unicast packet istransmitted to the receiving node 130, an ACK time interval 320indicates the time needed for the receiving node 130 to return the802.11 ACK corresponding to the first unicast packet and for the accesspoint 120 to process the 802.11 ACK packet.

Similarly, a second time interval 330 indicates the time needed for theaccess point 120 to convert the multicast packet received from thesource node 110 into the second unicast packet and transmit the secondunicast packet to the receiving node 140 at the second data rate, forexample, 18 Mbps. A second ACK time interval 340 indicates the timeneeded for the receiving node 140 to return an 802.11 ACK correspondingto the second unicast packet and for the access point 120 to process the802.11 ACK packet. In comparison, a multicast time interval 350indicates the duration for the access point 120 to receive and transmitthe multicast packet simultaneously to the receiving nodes 130 and 140at either the lowest common denominator rate or the minimum allowablephysical data rate.

Because the duration of the combined time intervals 310, 320, 330, and340 is shorter than the duration of the multicast time interval 350, thesystem and method described herein advantageously achieve a higher datathroughput by converting the multicast packet to sequential unicastpackets. Further, as the duration of the time intervals 310 and 320increases because of interference in the wireless links 135 and 145(FIG. 1) leading to lower first and second data rates, for example, thecombined duration of the time intervals 310, 320, 330, and 340 mayexceed the multicast time interval 350. In such case, the lowest commondenominator rate may provide a higher data rate than the minimumallowable data rate. Another advantage, therefore, is gracefuldegradation of the overall data transmission rate with changes in thewireless LAN.

The embodiments discussed herein are illustrative of one example of thepresent invention. As these embodiments of the present invention aredescribed with reference to illustrations, various modifications oradaptations of the methods and/or specific structures described maybecome apparent to those skilled in the art. All such modifications,adaptations, or variations that rely upon the teachings of the presentinvention, and through which these teachings have advanced the art, areconsidered to be within the scope of the present invention. Hence, thesedescriptions and drawings should not be considered in a limiting sense,as it is understood that the present invention is in no way limited toonly the embodiments illustrated. The scope of the invention should,therefore, be determined not with reference to the above description,but instead should be determined with reference to the appended claimsalong with their full scope of equivalents.

1. A method for improving throughput in a communications network, themethod comprising: receiving into an access point of the communicationsnetwork a multicast or broadcast packet from a source; determining afirst physical data rate by which the access point may transmit themulticast or broadcast packet to a first station associated with theaccess point; determining a second physical data rate by which theaccess point may transit the multicast or broadcast packet to a secondstation associated with the access point; and transmitting over thecommunications network the multicast or broadcast packet to the firststation and the second station at the lower of the first physical datarate and the second physical data rate.
 2. The method of claim 1,wherein the communications network comprises a wireless local areanetwork.
 3. The method of claim 1, wherein the multicast or broadcastpacket comprises a user datagram protocol networking message.
 4. Themethod of claim 1, wherein the multicast or broadcast packet comprises amulticast control packet.